Multiday Diving and Deep Safety Stops

The combination of dive computers and live-aboard dive vessels encourage multiday, multidive trips — and decompression sickness. In addition, taking a flight home soon after the dive trip multiplies the chance of problems.

Here are two important pieces to consider for your multiday diving. In the first, Steve Goble (Senior Hyperbaric Technician at the Royal Adelaide Hospital, Australia) and Dr. Lindsay Barker (with the Hospital’s Hyperbaric Medicine Unit) discuss the problems of putting deeper dives between shallower dives and taking deeper dives at the end, rather than the beginning, of the trip.

In the second, Aussie physician Geoff Gordon says the way we manage our safety stops may not be enough and, in fact, we need to rethink the way we go about diving. Both pieces are versions of articles that appeared in the Journal of the South Pacific Medicine Society, which we offer with their permission.

* * * *

Australian physicians studied 185 cases of DCI, sixty-two of which were related to multiday diving. While the mean was only six dives in four days, the ranges were 4-30 dives in 2-21 days. For example, one diver logged thirty dives over eight days to 100 feet, another dived as deep as 200 feet, 2-3 times a day for six days. And, another made five dives in three days, the last thirty-seven minutes at 100 feet, then flew home a few hours later.

Most of the divers noted at least two major symptoms; joint pain, headache and excessive fatigue. Typically, the symptoms appeared about thirteen hours after the last dive, but in some cases didn’t appear for four days. The average delay between onset and treatment was about 100 hours. Some symptoms went unnoticed or were ignored: skin tingling, numbness, problems with memory and thinking, and itching. Many patients were content to suffer from these “vague” symptoms for several days before realizing that they might have a problem and seek treatment.

When comparing multiday with single-day divers, the symptoms differed little. However, the singleday group noticed their symptoms on average six hours earlier than their multiday counterparts, and reported for treatment an average of thirty- nine hours earlier. About double the proportion of multiday divers used computers and about double the proportion (32 percent) took a flight after their last dive. Most of these did so within thirty- six hours and noted the appearance of symptoms while flying home.

The most common problem appears to be making deep dives between shallow dives. It was common to see the first dive to 60 feet, a second to 100 feet, and the third to 70 feet, for example. While computers calculate these types of profiles, doing your deep dive first and then doing progressively shallower dives reduces your risk.

Many live-aboard operations face the dilemma of whether to put deeper dives at the beginning or the end of the trip. If the deeper dives are at the end of a trip then the infrequent diver has a few days to polish up skills before moving on to deeper diving. However by diving deeper at the end of a trip, the diver is then at greater risk of DCI if he intends flying home within 24-36 hours.

A newly qualified diver or an infrequent club diver would probably be at a higher risk of DCI when participating in intense multiday diving trips. Just the increase in physical exercise and associated fatigue is likely to increase risk. Finally, divers need to realize that vague symptoms -- fatigue, itching, memory problems, etc. -- indicate a neurological problem that needs treatment immediately, not three days down the track.

* * * *

Our thinking regarding how we dive needs to change if we are to reduce the incidence of DCI in recreational diving.

The holy grail of no-stop diving may not be such a laudable goal after all. The data suggests that staged decompression after every dive will substantially reduce a diver’s risk of DCI.

While we see an increase in risk as dives get deeper, this effect is not nearly as great as with longer time. DCI can be expected to occur occasionally, even in relatively unprovocative exposures. Thus it should not be regarded as an accident because it does not always represent a loss of control.

Studies suggest that stops need to be made before significant bubbling has occurred if a benefit is to be realized. Spending, say, one minute at 60 feet, 2-3 minutes at 3O feet and 5-1O minutes at 15 feet after each dive should significantly reduce risk.

Can we trust recreational divers to discipline their diving to decrease DCI? Realistically I think not, as studies show an alarming number of divers who are unable to manage even their air supply. . . . However, I do hold out hope for those who have a genuine interest in reducing the risk of DCI in their dive practice, mainly us older, once bolder types.

The evidence is overwhelming for staged decompression -- even following a dive profile that, according to some algorithm, incurs no decompression debt. The objective after all is to reduce the probability of DCI to an acceptable minimum.